前言思路：
UIBezierPath是用来绘制动画路径的，真正显示的时候需要通过layer去显示，若要做对应的动画，则需要结合CAAnimation使用
绘制三角形
UIBezierPath *bezierPath = [[UIBezierPath alloc] init];
// 起始位置
[bezierPath moveToPoint:CGPointMake(0, 0)];
[bezierPath addLineToPoint:CGPointMake(100, 0)];
[bezierPath addLineToPoint:CGPointMake(100, 100)];
[bezierPath closePath];
// path路径，需要layer用来显示
CAShapeLayer *layer = [CAShapeLayer layer];
layer.path = bezierPath.CGPath;
// 路径围起后，内容的颜色
layer.fillColor = [UIColor redColor].CGColor;
// 线条颜色
layer.strokeColor = [UIColor blueColor].CGColor;
[self.view.layer addSublayer:layer];
系统方法绘圆
// 此刻拿到的是100，100的正方形，半径50则会变成圆
UIBezierPath *bezierPath = [UIBezierPath bezierPathWithRoundedRect:CGRectMake(0, 0, 100, 100) cornerRadius:50];
// path路径，需要layer用来显示
CAShapeLayer *layer = [CAShapeLayer layer];
layer.path = bezierPath.CGPath;
// 路径围起后，内容的颜色
layer.fillColor = [UIColor redColor].CGColor;
// 线条颜色
layer.strokeColor = [UIColor blueColor].CGColor;
[self.view.layer addSublayer:layer];
设置圆心，角度画圆（下图为对应的角度）
// 参数：圆点，半径，圆弧起始角度，圆弧终止角度，是否顺时针画
CGFloat startAngle = M_PI; // 起点为圆心的最左边
CGFloat endAngle = M_PI * 3 / 4; // 终点为起点的下面
// 绘制了3/4的圆
UIBezierPath *bezierPath = [UIBezierPath bezierPathWithArcCenter:CGPointMake(100, 100) radius:100 startAngle:startAngle endAngle:endAngle clockwise:true];
// path路径，需要layer用来显示
CAShapeLayer *layer = [CAShapeLayer layer];
layer.path = bezierPath.CGPath;
// 路径围起后，内容的颜色
layer.fillColor = [UIColor clearColor].CGColor;
// 线条颜色
layer.strokeColor = [UIColor blueColor].CGColor;
[self.view.layer addSublayer:layer];
角度.png
画曲线（一个控制点）
CGPoint starPoint = CGPointMake(100, 100);
CGPoint endPoint = CGPointMake(200, 100);
// 控制点
CGPoint controlPoint = CGPointMake(100, 50);
CALayer *layer1 = [[CALayer alloc] init];
layer1.frame = CGRectMake(starPoint.x, starPoint.y, 5, 5);
layer1.backgroundColor = [UIColor redColor].CGColor;
CALayer *layer2 = [[CALayer alloc] init];
layer2.frame = CGRectMake(endPoint.x, endPoint.y, 5, 5);
layer2.backgroundColor = [UIColor redColor].CGColor;
CALayer *layer3 = [[CALayer alloc] init];
layer3.frame = CGRectMake(controlPoint.x, controlPoint.y, 5, 5);
layer3.backgroundColor = [UIColor redColor].CGColor;
UIBezierPath *bezierPath = [UIBezierPath bezierPath];
// 绘制路径
[bezierPath moveToPoint:starPoint];
[bezierPath addQuadCurveToPoint:endPoint controlPoint:controlPoint];
// path路径，需要layer用来显示
CAShapeLayer *layer = [CAShapeLayer layer];
layer.path = bezierPath.CGPath;
// 路径围起后，内容的颜色
layer.fillColor = [UIColor clearColor].CGColor;
// 线条颜色
layer.strokeColor = [UIColor blueColor].CGColor;
[self.view.layer addSublayer:layer1];
[self.view.layer addSublayer:layer2];
[self.view.layer addSublayer:layer3];
[self.view.layer addSublayer:layer];
画曲线（两个控制点）
CGPoint starPoint = CGPointMake(100, 100);
CGPoint endPoint = CGPointMake(200, 100);
// 控制点
CGPoint controlPoint1 = CGPointMake(100, 50);
CGPoint controlPoint2 = CGPointMake(200, 150);
CALayer *layer1 = [[CALayer alloc] init];
layer1.frame = CGRectMake(starPoint.x, starPoint.y, 5, 5);
layer1.backgroundColor = [UIColor redColor].CGColor;
CALayer *layer2 = [[CALayer alloc] init];
layer2.frame = CGRectMake(endPoint.x, endPoint.y, 5, 5);
layer2.backgroundColor = [UIColor redColor].CGColor;
CALayer *layer3 = [[CALayer alloc] init];
layer3.frame = CGRectMake(controlPoint1.x, controlPoint1.y, 5, 5);
layer3.backgroundColor = [UIColor redColor].CGColor;
CALayer *layer4 = [[CALayer alloc] init];
layer4.frame = CGRectMake(controlPoint2.x, controlPoint2.y, 5, 5);
layer4.backgroundColor = [UIColor redColor].CGColor;
UIBezierPath *bezierPath = [UIBezierPath bezierPath];
// 绘制路径
[bezierPath moveToPoint:starPoint];
[bezierPath addCurveToPoint:endPoint controlPoint1:controlPoint1 controlPoint2:controlPoint2];
// path路径，需要layer用来显示
CAShapeLayer *layer = [CAShapeLayer layer];
layer.path = bezierPath.CGPath;
// 路径围起后，内容的颜色
layer.fillColor = [UIColor clearColor].CGColor;
// 线条颜色
layer.strokeColor = [UIColor blueColor].CGColor;
[self.view.layer addSublayer:layer1];
[self.view.layer addSublayer:layer2];
[self.view.layer addSublayer:layer3];
[self.view.layer addSublayer:layer4];
[self.view.layer addSublayer:layer];
画曲线的动画
CGPoint starPoint = CGPointMake(100, 100);
CGPoint endPoint = CGPointMake(200, 100);
// 控制点
CGPoint controlPoint1 = CGPointMake(100, 50);
CGPoint controlPoint2 = CGPointMake(200, 150);
CALayer *layer1 = [[CALayer alloc] init];
layer1.frame = CGRectMake(starPoint.x, starPoint.y, 5, 5);
layer1.backgroundColor = [UIColor redColor].CGColor;
CALayer *layer2 = [[CALayer alloc] init];
layer2.frame = CGRectMake(endPoint.x, endPoint.y, 5, 5);
layer2.backgroundColor = [UIColor redColor].CGColor;
CALayer *layer3 = [[CALayer alloc] init];
layer3.frame = CGRectMake(controlPoint1.x, controlPoint1.y, 5, 5);
layer3.backgroundColor = [UIColor redColor].CGColor;
CALayer *layer4 = [[CALayer alloc] init];
layer4.frame = CGRectMake(controlPoint2.x, controlPoint2.y, 5, 5);
layer4.backgroundColor = [UIColor redColor].CGColor;
UIBezierPath *bezierPath = [UIBezierPath bezierPath];
// 绘制路径
[bezierPath moveToPoint:starPoint];
[bezierPath addCurveToPoint:endPoint controlPoint1:controlPoint1 controlPoint2:controlPoint2];
// path路径，需要layer用来显示
CAShapeLayer *layer = [CAShapeLayer layer];
layer.path = bezierPath.CGPath;
// 路径围起后，内容的颜色
layer.fillColor = [UIColor clearColor].CGColor;
// 线条颜色
layer.strokeColor = [UIColor blueColor].CGColor;
/*
https://www.jianshu.com/p/5db371bb3fb7
strokeStart
默认是0，0~1过程中，相当于橡皮擦，擦线
strokeEnd
默认是1，0~1过程中，相当于画笔，画线
*/
layer.lineWidth = 5;
// 描述画线的过程
CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
animation.fromValue = @(0);
animation.toValue = @(1);
// 动画持续时间
animation.duration = 2;
[layer addAnimation:animation forKey:@"animation"];
[self.view.layer addSublayer:layer1];
[self.view.layer addSublayer:layer2];
[self.view.layer addSublayer:layer3];
[self.view.layer addSublayer:layer4];
[self.view.layer addSublayer:layer];
